/**
 * Copyright 2010-present Facebook.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.twodstar.photobattle;

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

import android.util.Log;

public class SntpClient 
{

    private static final int ORIGINATE_TIME_OFFSET = 24;
    private static final int RECEIVE_TIME_OFFSET = 32;
    private static final int TRANSMIT_TIME_OFFSET = 40;
    private static final int NTP_PACKET_SIZE = 48;

    private static final int NTP_PORT = 123;
    private static final int NTP_MODE_CLIENT = 3;
    private static final int NTP_VERSION = 3;

    // Number of seconds between Jan 1, 1900 and Jan 1, 1970
    // 70 years plus 17 leap days
    private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;

    // system time computed from NTP server response
    private long mNtpTime;

    // value of SystemClock.elapsedRealtime() corresponding to mNtpTime
    private long mNtpTimeReference;

    // round trip time in milliseconds
    private long mRoundTripTime;
    
     
    private static boolean m_IsSuccessful = false; 
    private static long m_RecordedUTC_Time = 0;
    private static long m_RecordedSystemTime = 0;
    
    /*
     * exmaple usage
    SntpClient client = new SntpClient();
    if (client.requestTime("pool.ntp.org", 30000)) 
    {
        long now = client.getNtpTime() + System.nanoTime() / 1000
                - client.getNtpTimeReference();
        Date current = new Date(now);
        System.out.println(current.toString());
    }
    */

    /**
     * Sends an SNTP request to the given host and processes the response.
     *
     * @param host
     *            host name of the server.
     * @param timeout
     *            network timeout in milliseconds.
     * @return true if the transaction was successful.
     */
    
    private static SntpClient m_Client = null;
    
    
    public static long GetTimeUTC()
    {
    	
    	if(m_Client == null)
    	{
    		m_Client = new SntpClient();
    		m_IsSuccessful = false;
    		
    		if (m_Client.requestTime("pool.ntp.org", 30000)) 
            {
            	m_IsSuccessful = true;
            	m_RecordedUTC_Time = m_Client.getNtpTime();
            	m_RecordedSystemTime = System.currentTimeMillis();
            	
                Log.i("game", "network time: " + m_RecordedUTC_Time);
                Log.i("game", "phone time: " + m_RecordedSystemTime);
                
                return m_RecordedUTC_Time;
            }
            
    	}
    	else if(m_IsSuccessful)
    	{
    		return m_RecordedUTC_Time + (System.currentTimeMillis() - m_RecordedSystemTime);
    	}
    	else
    	{
    		if (m_Client.requestTime("pool.ntp.org", 30000)) 
            {
            	m_IsSuccessful = true;
            	m_RecordedUTC_Time = m_Client.getNtpTime();
            	m_RecordedSystemTime = System.currentTimeMillis();   	               
                
                return m_RecordedUTC_Time;
            }
    	}
    	
        
        return 0;
    }
    
    public boolean requestTime(String host, int timeout)
    {
        try 
        {
            DatagramSocket socket = new DatagramSocket();
            socket.setSoTimeout(timeout);
            InetAddress address = InetAddress.getByName(host);
            byte[] buffer = new byte[NTP_PACKET_SIZE];
            DatagramPacket request = new DatagramPacket(buffer, buffer.length,
                    address, NTP_PORT);

            // set mode = 3 (client) and version = 3
            // mode is in low 3 bits of first byte
            // version is in bits 3-5 of first byte
            buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);

            // get current time and write it to the request packet
            long requestTime = System.currentTimeMillis();
            long requestTicks = System.nanoTime() / 1000;
            writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);

            socket.send(request);

            // read the response
            DatagramPacket response = new DatagramPacket(buffer, buffer.length);
            socket.receive(response);
            long responseTicks = System.nanoTime() / 1000;
            long responseTime = requestTime + (responseTicks - requestTicks);
            socket.close();

            // extract the results
            long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
            long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
            long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
            long roundTripTime = responseTicks - requestTicks
                    - (transmitTime - receiveTime);
            // receiveTime = originateTime + transit + skew
            // responseTime = transmitTime + transit - skew
            // clockOffset = ((receiveTime - originateTime) + (transmitTime -
            // responseTime))/2
            // = ((originateTime + transit + skew - originateTime) +
            // (transmitTime - (transmitTime + transit - skew)))/2
            // = ((transit + skew) + (transmitTime - transmitTime - transit +
            // skew))/2
            // = (transit + skew - transit + skew)/2
            // = (2 * skew)/2 = skew
            long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime)) / 2;
            // if (Config.LOGD) Log.d(TAG, "round trip: " + roundTripTime +
            // " ms");
            // if (Config.LOGD) Log.d(TAG, "clock offset: " + clockOffset +
            // " ms");

            // save our results - use the times on this side of the network
            // latency
            // (response rather than request time)
            mNtpTime = responseTime + clockOffset;
            mNtpTimeReference = responseTicks;
            mRoundTripTime = roundTripTime;
        } 
        catch (Exception e) 
        {

            return false;
        }

        return true;
    }

    /**
     * Returns the time computed from the NTP transaction.
     *
     * @return time value computed from NTP server response.
     */
    public long getNtpTime() {
        return mNtpTime;
    }

    /**
     * Returns the reference clock value (value of
     * SystemClock.elapsedRealtime()) corresponding to the NTP time.
     *
     * @return reference clock corresponding to the NTP time.
     */
    public long getNtpTimeReference() {
        return mNtpTimeReference;
    }

    /**
     * Returns the round trip time of the NTP transaction
     *
     * @return round trip time in milliseconds.
     */
    public long getRoundTripTime() {
        return mRoundTripTime;
    }

    /**
     * Reads an unsigned 32 bit big endian number from the given offset in the
     * buffer.
     */
    private long read32(byte[] buffer, int offset) {
        byte b0 = buffer[offset];
        byte b1 = buffer[offset + 1];
        byte b2 = buffer[offset + 2];
        byte b3 = buffer[offset + 3];

        // convert signed bytes to unsigned values
        int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
        int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
        int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
        int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);

        return ((long) i0 << 24) + ((long) i1 << 16) + ((long) i2 << 8)
                + (long) i3;
    }

    /**
     * Reads the NTP time stamp at the given offset in the buffer and returns it
     * as a system time (milliseconds since January 1, 1970).
     */
    private long readTimeStamp(byte[] buffer, int offset) {
        long seconds = read32(buffer, offset);
        long fraction = read32(buffer, offset + 4);
        return ((seconds - OFFSET_1900_TO_1970) * 1000)
                + ((fraction * 1000L) / 0x100000000L);
    }

    /**
     * Writes system time (milliseconds since January 1, 1970) as an NTP time
     * stamp at the given offset in the buffer.
     */
    private void writeTimeStamp(byte[] buffer, int offset, long time) {
        long seconds = time / 1000L;
        long milliseconds = time - seconds * 1000L;
        seconds += OFFSET_1900_TO_1970;

        // write seconds in big endian format
        buffer[offset++] = (byte) (seconds >> 24);
        buffer[offset++] = (byte) (seconds >> 16);
        buffer[offset++] = (byte) (seconds >> 8);
        buffer[offset++] = (byte) (seconds >> 0);

        long fraction = milliseconds * 0x100000000L / 1000L;
        // write fraction in big endian format
        buffer[offset++] = (byte) (fraction >> 24);
        buffer[offset++] = (byte) (fraction >> 16);
        buffer[offset++] = (byte) (fraction >> 8);
        // low order bits should be random data
        buffer[offset++] = (byte) (Math.random() * 255.0);
    }
}


